This invention relates to a speed governor for a vehicle equipped with an internal combustion engine which can limit the speed of the vehicle to a desired value. A speed governor according to the present invention is useful for preventing damage to the engine of a vehicle due to excessive rotational speeds. It can also be used to automatically limit the vehicle speed to any desired level, such as the legal speed limit of the road on which the vehicle is traveling.
A speed governor is a device which limits the speed of a vehicle to a prescribed level for purposes of safety and to prevent damage to the engine of the vehicle from operation at extremely high rotational speeds. One conventional speed governing method is to stop combustion in the engine for a continuous period from the point in time that the vehicle speed exceeds a prescribed level until the speed falls to an acceptable level. Combustion can be stopped by cutting off the supply of fuel to the cylinders or by cutting off the current to an ignition coil for igniting the spark plugs for the cylinders. However, this conventional method has a number of problems. One problem is that since combustion is continuously stopped until the vehicle speed falls to an acceptable level, the temperature of the engine cylinders falls due to cooling by intake air or fuel. Therefore, when combustion is restarted once the vehicle speed reaches the acceptable level, the cooled cylinders may be damaged by thermal shock. Furthermore, when combustion is suddenly stopped, the engine torque abruptly falls to zero, and this can produce jerking of the vehicle which degrades the comfort of the ride. In addition, when combustion is continuously stopped, uncombusted fuel is discharged from the engine in large quantities. Not only is the uncombusted fuel an environmental problem, but the fuel may undergo after-burning or post ignition which can damage the exhaust valves and other parts of the engine.